p-Benzoquinone is a valuable chemical intermediate which is used in the preparation of herbicides, dyes, photographic initiators and the like. It is also useful as an inhibitor in processing certain vinyl monomers such as acrylic acid and as a dehydrogenation agent. Other quinones such as methyl-p-benzoquinone, cyclohexyl-p-benzoquinone, phenyl-p-benzoquinone, o-benzoquinone, 1,4-naphthoquinone and the like are also valuable chemical intermediates.
One classical method of making p-benzoquinone involves the oxidation of aniline using manganese dioxide catalyst in the presence of water and sulfuric acid. This process produces substantial quantities of inorganic solid by-products.
Another process is concerned with the oxidation of phenol using oxygen or an oxygen containing gas in the presence of cuprous or cupric ions and selected metals including nickel, iron, tin, cobalt, chromium, molybdenum and magnesium (U.S. Pat. No. 4,208,339).
Because of the ready availability of hydroquinone, it would also be desirable to provide efficient catalytic processes for converting it to p-benzoquinone.
Classical methods for converting hydroquinone to p-benzoquinone include oxidation of hydroquinone in the presence of sodium chlorate, vanadium pentoxide, and sulfuric acid [Organic Syntheses, Coll. Vol. II, p. 553, John Wiley and Sons, New York (1943)] and by means of oxidation using sodium dichromate in sulfuric acid solution [Organic Syntheses, Coll. Vol. I, p. 482, John Wiley and Sons, New York (1941)]. These processes produce corrosive by-products which damage processing equipment and they are not desirable from an environmental standpoint. Also p-benzoquinone reacts with water at an appreciable rate. Thus, a catalytic process which does not produce objectionable by-products and which can be operated in a nonaqueous system would be highly desirable.
Other prior art of interest includes U.S. Pat. No. 3,213,114 which describes a process for preparing a 2,6-dialkyl p-benzoquinone (but not uhsubstituted p-benzoquinone) which involves oxidation of a 2,4,6-tri-tert-alkylphenol with oxygen using an oxidation catalyst. Unsupported platinum is mentioned, but it is taught that only 2,4,6-tri-tert-alkylphenols can be employed in the process.
French Patent 1,338,462 describes the oxidation of hydroquinone to p-benzoquinone at 80.degree. C. using oxygen in glacial acetic acid or propionic acid using 5% Ru or Rh supported on carbon. Also, in French Addition Patent 83,108 (1964) it is disclosed that water can be used as the solvent rather than acetic or propionic acid.
Finally, R. J. Radel et al., Ind. Eng. Chem. Prod. Res. Dev. 21, 566 (1982) reports on the use of Ru and Rh (but not Pt) for hydroquinone oxidation.
None of the prior art references teach the use of a supported platinum catalyst for preparation of quinones.